The statements in this section merely provide background information related to the present disclosure and may not constitute prior art.
Powertrain architectures comprise torque-generative devices, including internal combustion engines and electric machines, which transmit torque through a transmission device to an output. One exemplary transmission includes a two-mode, compound-split, electro-mechanical transmission which utilizes an input member for receiving motive torque from a prime mover power source, for example an internal combustion engine, and an output member for delivering motive torque from the transmission to a vehicle driveline. Electric machines, operable as motors or generators, generate a torque input to the transmission, independently of a torque input from the internal combustion engine. The electric machines may transform vehicle kinetic energy, transmitted through the vehicle driveline, to electrical energy potential that is storable in the electrical energy storage device. A control system monitors various inputs from the vehicle and the operator and provides operational control of the powertrain system, including controlling transmission gear shifting, controlling the torque-generative devices, and regulating the electrical power interchange between the electrical energy storage device and the electric machines.
The exemplary electro-mechanical transmission is selectively operative in a low range and a high range, which are descriptive of relative input/output speed ratios between the torque-generative devices and the output, i.e., the driveline. The low range and high range both preferably include continuously variable operation and fixed gear operation, the operation being controlled through selective application and release of torque-transfer clutches, via a hydraulic circuit. Fixed gear operation occurs when rotational speed of the transmission output member is a fixed ratio of rotational speed of the input member from the engine, due to application and release states of one or more torque transfer clutches. Continuously variable operation occurs when rotational speed of the transmission output member is variable based upon operating speeds of one or more of the electric machines.
The transmission is controlled in either the low range or the high range using a flow management valve, which transitions between a first position and second position in response to a command to shift operation to the low or high range. Anomalous operation in the hydraulic circuit or the flow management valve which results in the valve not transitioning can affect transmission operation, including a potential unintended application or release of one of the clutches.